Marine Weather and Tide Forecast for Danville, CA

SHORT TERM
(Today and tonight)
Issued at 238 AM PDT Thu May 22 2025

The marine layer is being observed at 800 feet by the Fort Ord profiler with satellite just starting to show some stratus forming over Tomales Bay and along the San Francisco Peninsula Coast.
Despite this, the 00Z KOAK sounding revealed a LowRH (surface-850 mb) value of 25%, a MidRH (850mb-650mb) value of 9%, and a precipitable water value of 0.45 inches which is slightly above the 10th percentile of 0.42 inches for 00Z May 22nd. An upper-level shortwave trough will skirt the region today, bringing temperatures back down to seasonal normals. Of more impact will be the strong onshore winds that it brings with gusts of 25-35 mph expected over the waters, along the immediate coastline, through northwest/southeast oriented valleys, and in the higher terrain.
These winds in conjunction with poor relative humidity (both overnight recovery and daytime minimum) will continue to support elevated fire weather conditions.

LONG TERM
(Friday through Wednesday)
Issued at 238 AM PDT Thu May 22 2025

An approaching second, deeper upper-level shortwave trough will deepen the marine layer and finally ease fire weather concerns for the time being as excellent relative humidity recovery (70%+)
returns to all but the highest terrain of the Central Coast.
Sensibly, temperatures will drop to 5 degrees below normal, dubbing tomorrow the coolest day of the week. Heights will begin to build and temperatures rebound to seasonal normals Saturday as a positively tilted upper-level longwave ridge builds into the West.
Due to the orientation of the upper-level pattern, the warmest day for the Bay Area will be Saturday with the Central Coast having to wait until Sunday to achieve that feat. The unofficial start of Summer (Memorial Day) will feel anything but with below normal temperatures brought to you by a dry cold front. The previously mentioned upper-level longwave ridge will build and broaden across the Western two-thirds of CONUS with an upper-level shortwave trough likely to undercut it, resulting in split flow and unimpactful weather for our region Tuesday and Wednesday.

AVIATION
(12Z TAFS)
Issued at 416 AM PDT Thu May 22 2025

VFR is expected to prevail with a dry airmass across our region in place. Local geographic effects are responsible for low stratus in the vicinity of the Monterey Bay terminals.

Vicinity of SFO...VFR is expected to persist through the day and evening hours with a chance of MVFR/IFR cigs late in the forecast period for early Friday. Confidence is too low for mentioning in the TAF attm. Gusty onshore winds will develop this afternoon and persist until after midnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals.. MVFR/IFR cigs early this morning due to local effects from an otter eddy in Monterey Bay. Short term guidance suggests that the low stratus will lift after 15z this morning and remain VFR until after midnight, when there is a chance for MVFR/IFR cigs developing in the early morning hours Friday.

MARINE
(Today through Tuesday)
Issued at 416 AM PDT Thu May 22 2025

Widespread hazardous marine conditions continue today as strong northwesterly breezes with near gale to gale force gusts and rough seas persist. Fresh to strong northwesterly breezes and moderate to rough seas will prevail Friday through Monday.

FIRE WEATHER
Issued at 238 AM PDT Thu May 22 2025

The combination of poor daytime relative humidity of 15-25% and onshore winds with gusts of 25-35 mph along the immediate coastline, in northwest/southeast oriented valleys, and in the higher terrain will continue to support elevated fire weather conditions today. The greatest period of concern is today in cured grass areas. Remain fire wise and do not be the reason for fire starts.

Sarment

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge.

Small Craft Advisory from 9 AM this morning to 3 AM PDT Friday for Mry Bay.

Small Craft Advisory until 3 PM PDT this afternoon for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Gale Warning from 3 PM this afternoon to 9 PM PDT this evening for Pt Pinos to Pt Piedras Blancas 0-10 nm.